Devices of the said kind are used in biology and medicine, for example, to store organic materials under specific external conditions.
Such devices for the cultivation and storage of microorganisms that can greatly accelerate their growth under special living conditions are widely found. In general, the temperature in these devices is, as an important growth parameter, kept constant at a certain level for a long time. However, there are also instances in which temperatures determined according to a preset temperature program are reached at certain times and kept constant for a certain time. These devices are frequently outfitted with heating devices and cooling units both for heating and cooling operation.
Temperature-controlled incubation devices or storage devices for storage of tissues are used in medicine.
It is very important for hygienic reasons that it be very easy to clean these devices. This is necessary in particular to prevent transmission of germs and undesired infections.
Various basic forms of incubation and storage devices are known in the prior art.
One distinguishes among the following systems:
1. Direct Evaporators for Cooling Agents and Electrical Heating Elements.
Here the electrical heating elements are brought to the inner container of the incubation device from outside or in rare cases are arranged in the inner space. Cooling takes place via the cooling agent evaporator, which is arranged directly in the internal space, for example. Alternatively, a part of the internal air is brought to the evaporator via a bypass and cooled before the cooled air is returned to the inner space of the incubation device.
A disadvantage of this known solution is that the two separate systems for heating and cooling the incubation device are very costly and difficult to control with regard to maintaining a preset temperature. The overlapping of cooling and heating is frequently very high because of the inertia of the individual systems so that tradeoffs involving the temperature constancy have to be made or costly control systems have to be installed. In particular, it is difficult to match the heating and cooling systems to each other so that temperature constancy with low deviation of temperature around a set point is achieved.
2. Indirect Cooling and Electrical Heating Elements
One such system is disclosed in DE 873892. In this case tubular heating elements in supports are arranged in the inner space and, according to one embodiment of the object of said invention, they can also be in part replaced by cooling tubes. Combined cooling and heating of the inner space is enabled through this.
Again, a disadvantage of this prior art is the costly control system in order to match the separate systems for heating and cooling the inner space of the incubation device to each other. Moreover, the supports, in which the heating elements or the cooling liquid is/are situated, are arranged in the inner space, which has a highly adverse effect on the cleaning capabilities when used in hygienically demanding applications in biology and medicine.
3. Water Jackets
With this system water is used as a heat carrier and circulates in a so-called “water jacket.” The water jacket in this case is arranged as a second container around the inner container. In this way the temperature constancy is in fact very good, but the system has extraordinarily high inertia. Temperature programs with short phases of different temperatures practically cannot be realized with this system. Moreover, there is also the disadvantage that this system cannot easily be cooled, since an evaporator will freeze up within a short time. For this reason these systems are suitable only for temperatures that are above room temperature and that can be obtained without a cooling system.
Another disadvantage of direct heating that may be pointed out is the fact that the electrical heating elements that are used produce a very high temperature with very low surface area, so that the heat is released to the air in the inner space of the incubation device through radiation and convection. However, since a temperature of only 37° C., for example, is required, flows of different temperature arise rather than the desired average value being established. Thus it is difficult not only from the standpoint of control technology but also flow technology to distribute the temperature uniformly in the inner space.